Two American presidents will make headlines in Europe tomorrow. President Trump meets with European leaders in Brussels. And former President Barack Obama makes his first major foreign appearance since leaving office. He and German Chancellor Angela Merkel will lead a public conversation at Berlin's Brandenburg Gate. It's part of a series of events marking the 500th anniversary of the Protestant Reformation. And it also marks a theme - civic engagement - that's emerging as one of President Obama's core concerns.

Heinrich Bedford-Strohm is Germany's top Protestant bishop. He invited President Obama to this event long before last year's election, and he will moderate tomorrow's discussion. I spoke with the bishop and asked him why he chose these two leaders, Merkel and Obama, to discuss the responsibilities of global citizenship.

HEINRICH BEDFORD-STROHM: The theme that we have chosen is the future of democracy, getting engaged in democracy. I think it's wonderful to have a leader who has had eight years in office speaking to another leader who is still in office about what are the guidelines? What are the basic orientations with which you go into politics? What are the ideals?

And how do you deal with your ideals when you're confronted with the dilemma situations in politics? And my hope is that especially young people have an incentive to get involved themselves. I think that's what we need most - an involved, engaged civil society in dialogue with politics.

MARTIN: Explain the religious underpinnings of this. You wrote recently that anyone who is pious also has to be politically minded.

BEDFORD-STROHM: Yes. This does, of course, not mean that you do party politics, but what it means is that you can never leave politics out if you take Christian faith seriously because Christian faith is about love of God and love of neighbor, both connected.

And if you also know that a lot of the misery of the difficult situations people are in has to do with political structures, has to do with decisions that are made either globally or nationally on the political level, then you know that alleviating their problems needs getting engaged into politics as well. And I think the churches, the religious communities have a duty to get engaged.

MARTIN: It's interesting also to note that there is another event similar to this one. It's called the Kirchentag. And this is an event that draws German protesters every year. It started out, as I understand it, after World War II as a way to confront and deal with the church's complacency during the Nazi regime.

BEDFORD-STROHM: Yes, exactly. Actually, the event with Barack Obama and Angela Merkel is part of the Kirchentag. It is designed to talk about faith, to worship, to get more spiritual strength but then also to discuss about the consequences for public life.

What you said is exactly true. It came from the experience that the churches in the time of National Socialism did not speak up enough when Jews were transported away, when political opponents, social democrats or other people were put into prison or into concentration camps. And there were some few people in the churches who spoke up, but most of the churches did not really speak up while a grave injustice was happening.

MARTIN: This year is special though because it's the 500th anniversary of the Protestant Reformation.

BEDFORD-STROHM: Yes.

MARTIN: And the Reformation was about giving people more control over their relationship with God, doing away with the idea that there had to be a middle man in the form of a priest. Is there a connection do you think between the symbolism of the Reformation and the idea of an empowered global citizenry?

BEDFORD-STROHM: I think there is actually. And I'm very happy to say that this is not something anymore which separates us from the Catholic Church or from other denominations. I call it, as Martin Luther, Christian liberty, the freedom of a Christian person. And that means you know in your heart that you are cared for by God, that God will protect you, that God will go with you no matter what happens. And that is why you do not have to fear authorities.

You do not have to fear disadvantages when you speak up, for example. So civil courage, something that, for example, Martin Luther King Jr. stands for, comes from this Christian liberty. It means that you have a firm inner strength to speak up with courage and at the same time to be an advocate for the poor and advocate for those who are marginalized and advocate for peace and overcoming violence. That is what Martin Luther described when you started Reformation and began a big movement that is now the basis for an ecumenical future.

MARTIN: Bishop Heinrich Bedford-Strohm. He is the leading Protestant bishop in Germany. Thank you so much for your time, Bishop.